1. Field of the Invention
The invention relates to a steering lock driving circuit and a steering lock device that restrict rotation of a steering shaft.
2. Description of Related Art
A vehicle is equipped with an antitheft lock mechanism that restricts (locks) rotation of a steering shaft. For example, when a passenger, or the like, rotates a steering wheel in a state where a mechanical key is removed from a key cylinder, rotation of the steering shaft is restricted. In addition, when an electronic key system in which a vehicle authenticates a key and allows engine start, or the like, is used, rotation of the steering shaft is restricted by the lock mechanism once a predetermined condition is satisfied (hereinafter, simply referred to as “steering is locked”). The latter is called electronic steering lock system.
FIG. 1 is a view that illustrates an example of a conventional electronic steering lock system. When an integrated microcomputer 230 acquires the authentication result that an electronic key is authenticated, the integrated microcomputer 230 outputs a lock power supply command from a lock power supply command port 330 to an AND circuit 430 on the condition that the ignition is off. A signal, which indicates “1” when a shift position is “P”, is supplied to the AND circuit 430 via an OR circuit 410. Thus, in FIG. 1, when the ignition is off and the shift position is “P”, steering is locked. It is presumable that the condition for locking steering is not satisfied while the vehicle is running, so the electronic steering lock system does not malfunction to lock steering while the vehicle is running.
In addition, a protection circuit 380 of FIG. 1 is not implemented by the software of the integrated ECU but implemented by a hardware circuit. Therefore, even when there is a malfunction in the operation of the integrated ECU (integrated microcomputer 230), the protection circuit 380 does not receive any influence, and is able to further accurately determine whether the condition for locking steering is satisfied.
In addition, when the integrated microcomputer 230 outputs an unlock signal to an OR circuit 420, steering lock is released. That is, steering lock is released even when the shift position is other than “P”.
However, in the circuit shown in FIG. 1, when the integrated microcomputer 230 is being started up or when there is a malfunction in the integrated microcomputer 230, the integrated microcomputer 230, for example, may erroneously outputs the unlock signal to the OR circuit 420 and steering lock may be released.
Such erroneous release of steering lock may be prevented in a case where the condition for releasing steering lock includes a state in which the shift position signal is “P”, as the condition for locking steering. However, in such a case, steering lock may not be released unless the shift position is “P”.
In conventional engine start using a mechanical key, engine start is allowed even when the shift position is “N”. On the other hand, in an electronic key system, steering lock is not released unless the shift position is “P”, so engine start is substantially not allowed unless the shift position is “P”. Therefore, some passengers may find it inconvenient.
In addition, even when a passenger tries to start the engine while setting the shift position in “P”, if the passenger changes the shift position quickly after the passenger presses down an engine switch (start button) (by successive operation), the shift position may be changed to “N”, or the like, other than “P”, on the way of release of steering lock. In this case, because the position of a lock bar that restricts rotation of the steering shaft has not reached the unlock position yet, the passenger may have to retry engine start.